Question

I have 2 models. A User and a Task. Here’s the code for them both:

class User < ActiveRecord::Base
  has_many :tasks
  has_many :assigned_tasks, :class_name => 'Task', :foreign_key => 'assigned_user_id'
end

class Task < ActiveRecord::Base
  belongs_to :user
  belongs_to :assigned_user, :class_name => 'User', :foreign_key => 'assigned_user_id'
end

The schema is quite obvious, but for consistency, this is how it looks:

ActiveRecord::Schema.define(:version => 20110925050945) do
  create_table "tasks", :force => true do |t|
    t.string   "name"
    t.integer  "user_id"
    t.integer  "assigned_user_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "users", :force => true do |t|
    t.string   "name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end
end

I’ve added a test case for the assigned_tasks relationship. It looks like this:

class UserTest < ActiveSupport::TestCase
  test "assigned tasks" do
    u1 = User.create(:name => 'john')
    u2 = User.create(:name => 'dave')

    assert_empty u2.assigned_tasks # LOOK AT ME

    task = u1.tasks.create(:name => 'some task', :assigned_user_id => u2.id)

    assert_equal 1, u2.assigned_tasks.size
  end
end

Now, this test case fails. It fails on the last assertion. If I remove the previous assertion (marked ‘LOOK AT ME’), this test passes fine. It also passes fine if I change this line to assert u2.assigned_tasks. Meaning it appears to break when, and only when, empty? is called against u2.assigned_tasks. Where that assertion passes, the following one fails. Here’s the failure:

UserTest:
     FAIL assigned tasks (0.12s) 
          <1> expected but was
<0>.
          test/unit/user_test.rb:12:in `block in <class:UserTest>'

So, it appears once empty? is called on the original u2.assigned_tasks Array, the task is not actually added/associated with it’s assigned user. This however appears to work fine in console.

Apologies if I’m completely overlooking something simple here, but I really can’t make any sense of this. Any points in the right direction would be extremely helpful. Thanks

PS: Rails 3.1 with a vanilla application

Answer 1

You need to reload the assigned_tasks, or u2.

# This line causes assigned_tasks to be loaded and cached on u2.  Not the calling
# of empty?, but rather the loading of the association.
assert_empty u2.assigned_tasks

# but then you actually make the task here
task = u1.tasks.create(:name => 'some task', :assigned_user_id => u2.id)

# so when this assertion happens, u2 already has an empty set of tasks cached, 
# and fails
assert_equal 1, u2.assigned_tasks.size

# however either of these should pass
assert_equal 1, u2.assigned_tasks(true).size
assert_equal 1, u2.reload.assigned_tasks.size

The inverse_of option serves to improve in-memory association behavior, and might also solve your problem (without reloading). Read about that here. It would look something like this (but again I’m not positive it will work in this case):

# on User
has_many :assigned_tasks, ..., :inverse_of => :assigned_user

# on Task
belongs_to :assigned_user, ..., :inverse_of => :assigned_tasks

# in your test you might have to change the task creation to:
u1.tasks.create(:name => 'some task', :assigned_user => u2)